System and method for converging iterations in a hybrid loadflow computer arrangement

ABSTRACT

A hybrid loadflow computer arrangement includes an analog network simulator and a digital computer which acquires and processes on-line data and operator data related to the power system for which a loadflow problem is being solved. The analog simulator includes modular circuits representative of power system busses and lines and the interface between the digital computer and the analog network simulator is provided by analogto-digital and digital-to-analog converters and by line outage contact closure outputs. The hybrid arrangement operates iteratively, with the analog network simulator providing a bus voltage solution for a set of network simultaneous equations and the digital computer providing bus load and generation injection current calculations and convergence steering control. To converge the solution, the digital computer is programmed to change the generation reactive power at voltage regulated busses in each iteration as a function of the difference between the analog computed bus voltage and a specified bus voltage.

United States Patent [1 1 Enns et al.

[4 1 Sept. 2, 1975 [75] Inventors: Mark K. Enns, Ann Arbor, Mich.;

Jorge E. Petit, Bethel Park, Pa; Jerry C. Russell, Minneapolis,

Minn.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Aug. 26, 1971 [2]] Appl. No.: 175,289

[52] U.S. Cl. 235/l5l.21; 444/1; 307/43;

235/184 [51] Int. Cl. G06G 7/62; HOSK l/OO [58] Field of Search 235/l5l.2l, 150.5, 184,

[56] References Cited OTHER PUBLICATIONS Computer Control of Electrical Distribution, Control, November 1964, pp. 589-591.

Computer Control of Power Systems," The Engineer, October 2, 1964.

Considerations in the Regulation of Interconnected Areas, IEEE Transactions on Power Apparatus and Systems, December 1967, pp. 1527-1539.

Primary ExaminerEdward J. Wise Attorney, Agent, or FirmE. F. Possessky [5 7] ABSTRACT A hybrid loadflow computer arrangement includes an analog network simulator and a digital computer which acquires and processes on-line data and operator datarelated to the power system for which'a loadflow problem is being solved. The analog simulator includes modular circuits representative of power system busses and lines and the interface between the digital computer and the analog network simulator is provided by analog-to-digital and digital-to-analog converters and byline outage contact closure outputs. The hybrid arrangement operates iteratively, with the analog network simulator providing a bus voltage solution for a set of network simultaneous equations and the digital computer providing bus load and generation injection current calculations and convergence steering control. To converge the solution, the digital computer is programmed to change the generation reactive power at voltage regulated busses in each iteration as a function of the difference between the analog computed bus voltage and a specified bus voltage.

13 Claims, 44 Drawing Figures ANALOG 66 302 NETWORK SENSORS/ SIMULATOR v GROUP 64 ||2 no a l EW HAMPSHIRE DATA ACQUISITION REGMNAL GROUP %H%%RVISORYM PERI PHERALS SECURITY COMPUTER C SYSTE COMPUTER L 68 CONTROLLABLE SHARED I 72 DEVICES M ll ng Y GROUP DATA r aste m 70 74 SE A/213R 8%? COMPUTER COMPUTER 60 SENSORS PI'ITENTEU IP 2M5 SHEET 5 66 ANALOG 302w NETWORK SENSORS/ SIMULATOR 25 /62 DATAGEPQULZSITION NEW HAMPSHIRE PERIPHERALS SECURITY COMPUTER COMPUTER 68 l|3 CONTROLLABLE SHARED 1 72 w DEV'CES CORE GROUP DATA MEMORY gws T gn F REGIONAL MAINE DISPATCH GROUP 4 SENSORS COMPUTER COMPUTER 6O ANALOG NETWORK SIMULATOR IIO\ I REGIONAL PERIPHERALS SECURITY COMPUTER 1 EQQE O FIG .3 A MEMORY III 204 REGIONAL REGIONAL DATA DISPATCH ACQUISITION COMPUTER 2 SYSTEMS NOTE: FIRST ITEM IN BLOCI IS METER POINT FIGSC F|G.3D mg;

ee ITEMS INCLUDED IN BACKUP TELEMETERING SYSTEM m DATA CHANNELS BETWEEN NEPEx AND SATELLITES PIGSE TELEMETERED TO SATELLITE FROM METERING POINT ANALOG DATA RELAYED TO NEPEX AND NYPP FIGSF FIG.3B

PATENTEU 2 SHEET 6 ,236 REMvEC AREA TIEs TO NY. 8 G ,234

PRATTS JCT M/w OR-NEW BRUNSWICK PLATTSBURGH ROTTERDAM E205 ESSEX K22 MW MW MyfiI RUNBIOUT) T [238 f CONvEx AREA TIEs TO NY.

WHITEHALL GREENBUSH NORWALK RUTHLAND K7 DOREEN F132 NORTH RT I385 MW MW MW r- MVAR I MVAR MWHR(|N & OUT) MWHR(IN & OUT) HOOSIC I NEW SCOTLAND l m W3 NORTHFIED 393 MW MVAR MWHRIINGOUTI 2W5? aOUT) W PLEASANT VALLEY ADAMS SOUTHINGTON 398 MW MW I MvAR I MvAR /--MWIIR(IN 8IOUT MWHRIIN STOUT) ANALOG ANALOG LMETERINGW-=- METERING III III III-III X 220 W Y RK m m NEW ENGLAND NE 0 POWER (NYPP) (N EPEX) 25 NET DIGITAL IN TERCHANGE COMPUTER I MONTACHE NORTHEIELD DIAGRAM TIE To EMvEC STATION BOARD OR B128 81 H7? GENERATlON MW sPl-AY MW I GENERATION MW HR/HR MT TOM PUMP LOAD MW 2IO \zlz (-PUMP LOAD MW HR/HR UNIT 1 MW LUDLOW UPPER POND 345/H5 KV TR PE I FQJJXQEQ FT FAIRMONT MW T RIVERFLO CFS VOLTAGE(345KV) ALL ITEMS CARPENTERHILL F w -gzffig 3 Kv) MARED 30| MW MW MvAR MvAR BACKUP N W LUDLOW 354 TELEMETERING WLSPRINGFIELD MW SYSTEM UNITS-I23 WAR \206 gIzamMw CONVEX DIGITAL COMPUTER LKKKLRLLJJJJJJJJ I I'ITENTED 2 I975 3, 903 399 SHEET MERRIMAOK MANCHESTER SCOBIE Mw Hz SANDY POND 326 i MW TOTAL SATELLITE MW II MVAR GENERATION MVAR 2MvAR ggmkgfgg POWNAL 39l VOLTAGE IIIS KV) ACTUAL MW DUNBARTON A253 NET INTERCHANGE MvAR MW I. ME.YANK.385 MVAR MW MvAR VT. MW MVAR VOLTAGE(345KV) 345/ll5KV TR MW MvAR MONADNOCK 62 w; To NEES POWER STATION fifirf g MVAR NEW HAMPHIRE 4 M N 5 HUDSON 6 IRE TONEES Ylsl 8 DIGITAL COMPUTER u 3 WAR II II MvAR l g ll 6 ll GARVINS VOLTAGE l|5KV VOLTAGEI|5KV THREE RIv ERS- WHITEFIELD TIE TO CMP VOLTAGE H5 KV (250a I97 TOTAL) I: MW WEBSTER MVAR VOLTAGE 2'4 ZO8TEL%IRACEKFUEFI,RING 'TEMS SYSTEM MARKED 6i- 2|6 J YAR MOUTH 222 BUCKSPORT I (209 UNIT I Mw TIE TO BANGOR BACKUP ALL ITEMS TELEMETERING 2 HYDRO 2 SYSTEM MARKEDSK- 3 22 NETWIR POWNAL MASON 345/"5 KV TR. UNIT3 Mw 226 MW(H5KV) 4 MVARUISKV) n 5 n 345/ll5 KV TR. GUILFORD r MW(| I5KV) m TO BANGOR HYD. CENTRAL MAINE POWER MvAR(II5Kv) MvAR (0MP) 228 MAINE YANKEE HARRIS HYDRO COMPUTER um I Mw UNITS VOvLVTEg37475 KV) 1,2 a 3 MW ZR MvAR WYMAN HYDRO BANGOR MW ETQE MW WAR FIG.3 D 3* AuGuSTA HZ BANGOR-NEW BRUNSWICK TOTAL SATELLITE M GENERATION MW TOTAL cONTROL GENERATION ACTUAL SATELLITE NET INTEROHANGE PATENTEU 75 SHEET 10 505 534 PROGRAMMER'S ,509

CONSOLE PAPER TAPE A CRT I TYPEWRITER PUNCH 53g 50| SREADER f5 CRWZ CARD PUNCH PROCRAMMER'S 535 a READER CONSOLE k I TYPEwRITER PUBLIC CRT /503 52a 7 CARD PUNCH ALARM EI "3 4 TYPEwRITER k 530 532 SECURITY DISPATCH 1I T IIEF PAINTE PRINTER PROCESSOR MEMORY PROCESSOR 5B HO LOG ANALOG 50o TYPEwRITER NETWORK INPUT/OUTPUT S MULATOR INTERFACE 5|7 PUSH PANELS BUTTON CONSOLE LINE 502 OUT/GE T INPUT/OUTPUT fi 'Il'if If T SSR ERR CARD PUNCH /496 a READER DATA ANALOG/DIGITAL CONVERTER T F |G.4 A

MEMORYORGANIZATION I 5 I FOREGROUND s22- FOREGROUND SECURITY COMPUTER SSM COMMON SHARED SECURITY I I3 CORE 8. DISPATCH MEMORY COMPUTERS FOREGROUND REAL BUS VOLTAGE OUTPUTS IMAGINARY ClOl RIOI

RIO4

RIOS

PATENTED 2 975 lMAGlNARY LINES CUR ENT INPUTS RIO? H9 HIO Hll

PATENTEUSEP 2l975 3,903,399

REAL BUS FlGjA VOLT INPUT I I AR I I IMAGIN RH8 BUS v 1. INPUT T 0102 a l I it 3 a I PATENTEDSEP 21975 3,903,399

SHEET 16 INJECTION CURRENT H|6o-- wv-o 1 R k z CURRENTS 3 3 UMAGINARWOUT 3 e REF. VOLTAGE OUT (TO LINES) F IGS FROM 1/0 T0 o 1 LINE i FROM BUS LINE u MODULE FROM I/O :IMODULET FROM I/O FROM k FROM FROM To [/0 U0 U0 BUS 4 LINE 1 FROM MODULE BUS BUS FROM I /O F (TRANSFORMER) LINE' J i l MODULE TO FROM BUS BUS BUS FROM 1/0 -MODULE BLOS PATEHTEDSEP 2I975 3, 903 399 sIIEEI' I7 CONVEX REMVEC NH MAINE NEPEX ACTION BUTTONS VERIFY ENTER OUTPUT CANCEL CLEAR CONSOLE CRT DIGITAL DEVICE TYPER DISPLAY ON/OFF CRT UP DATE INHIBIT DEcIMAL I 2 3 PT PATENTED SEP 2 I975 SHEET 

1. A hybrid loadflow computer arrangement comprising a DC analog simulator of an AC network, said simulator including a plurality of bus DC circuits and line DC circuits interconnected to correspond to the AC network, digital means for generating bus generation and load current values as a function of predetermined parameters including stored bus power and voltage data, an analog output system for converting digital outputs to analog outputs, said digital means including means for causing said analog output system to generate phasor current signals representative of the digitally determined bus generation and load currents, means for applying the phasor bus geneRation and load current signals to the corresponding bus DC circuits, each of said bus DC circuits including means for responding to line phasor current and bus generation and load phasor input current signals and for generating an output bus voltage phasor signal, each of said line DC circuits including means for responding to the difference between applied bus voltage phasor signals and generating an output line phasor current signal in accordance at least with a representation of the equivalent series branch line impedance, means for applying bus voltage phasor signals to said digital means said digital means generating bus generation and load current values in successive iterations after a startup iteration as a function of bus voltage values determined in the next preceding iteration, said digital means further generating the bus generation and load current values as a function of bus reactive powers, means for generating new voltage regulated bus reactive power values in each iteration as a function of computed bus voltage signal representations from the last iteration so as to converge the iterative process to a solution, and means for sensing when a solution is reached.
 2. A hybrid overflow computer arrangement as set forth in claim 1 wherein said digital means is a programmed digital computer and said digital computer having means for controlling its sequential programmed operation including the programmed operation of said digital generating means, said sensing means, and said analog causing means.
 3. A hybrid loadflow computer arrangement as set forth in claim 2 wherein said digital computer further includes means for generating specified voltages for the network busses including acquired on-line voltage values for at least some of the busses, means for differencing at least voltage regulated bus voltage signal representations with the respective specified bus voltages, and means for determining the voltage regulated bus reactive power values as a function of the voltage differences for the voltage regulated busses.
 4. A hybrid overflow computer arrangement as set forth in claim 3 wherein the convergence function includes a predetermined gain factor for each voltage regulated bus.
 5. A hybrid overflow computer arrangement as set forth in claim 4 wherein the gain factor includes one element having a value common to all voltage regulated busses and another element having a value dependent on the maximum real power generation capability of the respective voltage regulated busses.
 6. A hybrid loadflow computer arrangement as set forth in claim 4 wherein the bus gain factor is multiplied against the bus voltage differences.
 7. A hybrid loadflow computer arrangement as set forth in claim 4 wherein bus generation and load currents are determined by the quantity Pp-jQpk divided by the quantity Epk conjugate.
 8. A hybrid loadflow computer arrangement as set forth in claim 2 wherein the convergence function includes a predetermined gain factor for each voltage regulated bus.
 9. A hybrid loadflow computer arrangement as set forth in claim 8 wherein the gain factor includes one element having a value common to all voltage regulated busses and another element having a value dependent on the maximum real power generation capability of the respective voltage regulated busses.
 10. A hybrid loadflow computer arrangement as set forth in claim 2 wherein said digital computer further includes means for retaining voltage regulated bus reactive power within limits as the solution is converged.
 11. A hybrid loadflow computer arrangement as set forth in claim 2 wherein said digital computer further includes means for setting the last on-line solution values of the bus voltage signal representations and the voltage regulated bus reactive powers as the corresponding initial values in the first iteration of a new on-line solution.
 12. An automated method for making on-line loadflow solUtions for an electric power system, the steps of said method comprising sensing representations of at least some on-line values including at least some on-line unit generation power and bus voltage values for the system, storing said on-line values in a programmed digital computer operating the digital computer to generate bus generation and load currents as a function of stored bus power and voltage data, applying phasor signals corresponding to the bus generation and load currents to an analog network simulator which includes DC bus circuits and DC line circuits interconnected to simulate the power system, operating the analog simulator to cause the bus circuits to generate solution bus voltage phasor signals, and operating the digital computer to generate new bus generation and load current values as a function of the stored data and the solution bus voltage phasor signals, operating said digital computer further to generate the bus generation and load current values as a function of bus reactive powers, operating said digital computer to generate new voltage regulated bus reactive power values in each iteration as a function of computed bus voltage signal representations from the last iteration so as to converge the iterative process to a solution, operating said digital computer to sense when a solution is reached, and sequentially controlling the operation of the digital computer in the performance of its program steps.
 13. A method as set forth in claim 12 wherein the method steps further comprise operating said digital computer to generate specified voltage values for the network busses including acquired on-line voltage values for at least some of the busses, operating said digital computer to difference at least voltage regulated bus voltage signal representations with the respective specified bus voltage values, and generating the voltage regulated bus reactive power values as a function of the voltage differences for the voltage regulated busses. 